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<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let arr = [];
        for (var i = 0; i < 5; i++) {
            (function (a){
                arr[a] = function () {
                console.log(a)
            }           
            })(i)           
        }
        // console.log(arr);
        console.log(arr[3]()) // 3
    </script>
</body>

</html>